The present invention relates generally to regulation of the speed of a spindle motor in a disc drive, and more particularly to a hardware based dedicated circuit to ensure that the heads on the actuator arm retract to the landing zone on the occurrence of an unexpected over speed or under speed of the spindle motor.
In a typical disc drive, there is one or more discs mounted on a spindle. The disc surface is divided into concentric tracks where data can be stored. Both sided of a disc provide for data storage. When data is to be retrieved or stored, a read/write head is used. The read/write head is mounted on a finger, which is in turn mounted on to the end of an actuator arm. The number of read/write heads is double of the total number of discs in a disc drive. The spindle is driven by the spindle motor to rotate the discs. The actuator arm is driven by VCM (Voice Coil Motor) to pivotally position the head over the disc surface such that it flies over the disc surface above a thin layer of air during operation. The read/write head and the disc surface are kept apart by the air bearing between them. When the spindle speed slows down such that the air bearing can not be sustained, the read/write head will tend to crash into and drag along the surface. This will cause permanent damage to the disc surface. Such situations usually occur during spindle start-up and spindle turn-off.
All modern disc drives have some means of preventing a read/write head of an actuator from crashing into the disc surface when there is either an intentional or emergency power shut-down. Actuators are typically moved to a non-data storage area on the disc surface during a power shutdown. Such an area on the disc surface is known as the landing zone where the actuator is parked when there is no read/write operation.
U.S. Pat. No. 4,371,903 issued on Feb. 1, 1983 to DMA Systems Corporation entitled xe2x80x9cEMERGENCY HEAD RETRACT SYSTEM FOR MAGNETIC DISC DRIVESxe2x80x9d, U.S. Pat. No. 4,786,995 issued on Nov. 22, 1988 and U.S. Pat. No. 4,866,554 issued on Sep. 12, 1989 to Peripheral Technologies, Inc. both entitled xe2x80x9cAUTOMATIC HEAD RETRACT SYSTEMxe2x80x9d teach how the problem of damage to the disc drive surface can be minimized.
U.S. Pat. No. 4,371,903 provides an electrical circuit with a switch means which is operatively positioned between the stator winding of a magnetic DC motor and a linear motor positioner coil (also known as Voice Coil). The magnetic DC motor is used as the spindle motor during normal operation. When an emergency situation arise, the switch means will couple the coil to the stator windings and relay means responsive to the emergency situation where the kinetic energy from the spindle mass is used to unload the read/write head.
U.S. Pat. No. 4,786,995 and U.S. Pat. No. 4,866,554 provide a latching system to retract the read/write head to the landing zone in response to electric power turn off (whether intentional or attributable to an emergency condition involving electric power loss). The read/write head is automatically retracted by operating the positioner motor (also known as the Voice Coil Motor) under the control of logic within the disc drive unit so as to control the speed of the carriage to avoid high speed crashing against its travel limit.
The means of managing retract of the read/write head are taught in the prior art mentioned above. In these prior art, the retract of the read/write head is in response to a power loss or an emergency situation. However, there is another aspect that would lead to the read/write head crashing into the disc surface. This involves the risk of abnormalities in the speed of the spindle motor. Such abnormalities are caused by the unexpected over or under speed of the spindle motor.
In the latest generation of disc drives, the spindle speed is regulated by the servo processor, which also controls the actuator. There are situations where the servo processor unexpectedly stops monitoring and controlling the spindle speed. These abnormalities may occur when the processor gets stuck in a loop or when the processor unexpectedly moves to a state where it expects not to have to monitor the spindle speed. The occurrence of such abnormalities increase as the code driving these processors becomes more complex. When spindle speed regulation is lost, the spindle speed invariably increases or decreases beyond a reasonable range. Early detection of abnormalities in the spindle speed has been used such that action may be taken to prevent the head from crashing into the disc surface by moving the actuator to the landing zone. U.S. Pat. No. 4,807,062 issued Feb. 21, 1989 to Kabushiki Kaisha Toshiba, entitled xe2x80x9cMULTIPLE FORCE RETRACT CIRCUIT FOR A MAGNETIC DISC DRIVExe2x80x9d describes a magnetic disc drive which provides for the magnetic head to move to the landing zone under abnormal conditions of the spindle motor. The magnetic disc drive has an abnormality detection means for detecting whether the drive is in an abnormal condition, a position detection circuit for detecting whether the magnetic head is at the landing zone, a control means and drive means to move the magnetic head, if it is not already at the landing zone. A microprocessor and many other elements in the whole circuit are used to ensure that the actuator is parked at the landing zone when abnormality arises.
There remain a need for an improved method to detect abnormalities of the spindle speed such that the servo processor recover from such situations even if it were in a loop or in an unexpected state.
There is also a need for a simple retract circuit for moving the actuator arm to the xe2x80x9clanding zonexe2x80x9d during abnormalities in the spindle speed where the servo processor is interrupted by a hardware mechanism to reset the servo processor to a known state. From such a known state, to servo processor should then be able to sense the spindle speed and lock to he spindle speed for speed regulation, or failing which, it should be able to brake the spindle and restart the power up procedure to restore spindle control. This will be a graceful way of recovering from an unexpected situation where spindle speed regulation is lost, and the servo processor is not aware of the loss of spindle speed regulation. It will be evident from the following description that the present invention offers this and other advantages.
The present invention is directed to minimize the above-mentioned problems with an improved retract system for an actuator in a disc drive. The actuator is retracted when spindle motor is under speed or over speed. According to the present invention, there is provided a disc drive with
The present invention provides a check of the spindle speed to minimize abnormalities in addition to the sudden slowing down or speeding up of the spindle speed either in an intentional and emergency power turn-off. Abnormalities are detected by setting a fixed range for comparing to the spindle motor speed of an operating disc drive such that a spindle motor will function without causing the read/write head to crash into the disc drive surface within that range.
The present invention can also be implemented in a disc drive a disc on a spindle, such that the spindle is rotatably driven by a motor at a spindle speed monitored by a frequency sensor. The disc drive also has a head for reading and writing data on a surface of the disc. The head being suspended from an actuator arm over the disc which is driven by a voice coil motor. The disc drive includes a retract device that has a comparator circuit to compare input signal from the frequency sensor with a predefined threshold range and outputs a comparison signal when the input signal falls outside of the predefined threshold range. The retract device also includes a delay filter which determine a duration of the comparator signal. A trigger initiates a retract mechanism when the comparison signal falls outside of the predefined threshold range for a predetermined duration of time. The retract mechanism being configured to move the head away from the surface of the disc.
The retract device has a comparator system to compare input signal from the frequency device with a predefined threshold range. There is also a delay filter to determine signal duration from the comparator system. A trigger is also included to initiate a retract mechanism when there is a resultant signal from the delay filter.
In another aspect of the present invention, the retract device having a circuit with a frequency-voltage converter, a comparator system, a delay filter and a trigger. The frequency-voltage converter in the circuit converts input frequency to voltage output to the comparator system where the voltage is compared with a predefined higher and lower threshold voltage range. The delay filter determines if the duration of the voltage supply from the comparator system is significant to be considered as an abnormality. This is achieved by comparing the duration of the voltage supply with a predefined threshold value set in the delay filter. If the duration of the voltage supply exceed the predefined threshold value, the voltage from the delay filter will simultaneously interrupt a processor and initiate a retract mechanism through the trigger.
In another embodiment of the present invention, the comparator system in the circuit has two comparators to determine if the voltage is within the threshold range; where one comparator is set at a higher threshold value and the other is set at a lower threshold value. To facilitate such a comparison, the voltage output from the frequency-voltage converter split into the two comparators. In order to obtain a single resultant output, an OR gate is incorporated into the comparator system to link the two comparators.
In another embodiment of the present invention, a low pass filter is used to provide a time delay as part of the delay filter. The low pass is made up of a resistor and a capacitor. There is also a fast discharge path linked to the OR gate of the comparator system during a low output. A third comparator, set at a predefined threshold value, is used to provide an adjustable delay value in the delay filter. It is preferred that the delay filter includes an AND logic gate to provide a single resultant output from the third comparator and the OR gate.
In yet another embodiment of the present invention, the signal processor is reset to a known state following the interruption such that it is enabled to restart the power-up procedure to restore spindle control.
In the present invention, the retract mechanism is initiated to enable the actuator to return to the landing zone.
One advantage of the present invention is that it is able to initiate two actions at the same time with a single resultant from a two-step process.
Another advantage of the present invention is that it provides a filter of non-genuine abnormalities like noise disturbances.